I'm in Michigan-- and we get them bad here because we "fit the criteria"...
they are the worst whereever you have a perfect combo of higher temps, dry conditions, sandy soil (outdoors) and a lot of agricultural activity nearby- like Farms , Orchards and vinyards.
That is because because THEY spray chemicals to rid their crops of ALL living things-- so the mites/thrips etc... go away from that area to find ANY food source they can take advantage of... mainly- your grow room!
No rain, perfect temps and lots of food without all the Monsanto crap being sprayed!
This is also why, once you get them (if in an AG area) they are harder to get rid of, because they have already built-up a tolerance to mitacides/pesticides... so Organics are less likely to work well.